Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $98.82   3.526%   $102.3044   $102.30   $102.30   $102.30  
  Purchase #2 $163.63   6.511%   $174.2839   $174.28   $174.30   $174.30  
  Purchase #3 $107.37   12.452%   $120.7397   $120.74   $120.75   $120.70  
  Purchase #4 $200.69   9.296%   $219.3461   $219.35   $219.35   $219.30  
  Purchase #5 $54.57   7.517%   $58.672   $58.67   $58.65   $58.70  
  Purchase #6 $152.40   3.614%   $157.9077   $157.91   $157.90   $157.90  
  Purchase #7 $171.90   10.515%   $189.9753   $189.98   $190.00   $190.00  
  7 purchase totals = $949.38       $1,023.2291   $1,023.23   $1,023.25   $1,023.20